cmake: Remove FindCapnProto.cmake
cmake: Remove FindCapnProto.cmake

This file is obsoleted by the CMake config package files that the autotools build now installs. Since FindCapnProto.cmake contains an implementation of capnp_generate_cpp(), in which I just fixed a bug, this file seems like a maintenance liability  now, so I'd like to delete it.

mologie/capnproto,mologie/capnproto,mologie/capnproto